Bug#1041201: FTBFS when libscotchparmetis-dev is installed

[Drew Parsons]

Source: freefem++
Version: 4.15+dfsg-1
Followup-For: Bug #1041201
Control: tags -1 ftbfs

Adding a conflict will workaround the issue,

but I see this as a bug in the freefem++ configuration scripts. They're
detecting the availability of parmetis (via scotch emulation in this
case) but they are not at the same time setting up the corresponding
include path to parmetis.h.